The present invention relates to a device for changing reels of strip material on a production machine.
The present invention is especially suitable for use on packing machines, particularly cigarette packing machines, to which the following description refers purely by way of example.
For special purposes, such as inner wrappings, cigarette packing machines employ a strip of foil fed off a reel and subsequently cut into portions from which the inner wrappings are formed. As it is about to run out, the reel is changed as described, for example, in Italian Patent Application N. 3473A/90, the content of which is included herein as required by way of reference.
According to the above method, a strip feed device is provided whereby the runout reel, supported on a spindle, is wound off by a traction device by which it is guided along a path comprising a first and second branch forming a given angle of other than 180.degree.; and a second identical strip is wound off a standby reel along the first branch of said path by means of a centerless unwinding device on which the standby reel is arranged on edge. As the first strip is about to run out, the unwinding device rotates the standby reel so as to accelerate the second strip up to the speed of the first; the first strip is cut upstream from the traction device; the second strip is cut along the first branch and fed on to the traction device; and the tail end of the first strip is discarded.
At this point, a transfer device provides for removing the empty reel and replacing it with the standby reel being unwound, e.g. by means of a swing arm with a spindle for unloading the standby reel off the centerless unwinding device, which may thus be loaded with a new standby reel.
The above system presents several drawbacks, foremost of which is the difficulty encountered in picking up the standby reel as it is being unwound, due to possible misalignment of the swing arm spindle and the reel. Secondly, to pick up the standby reel, the swing arm spindle must be fitted through practically the whole length of the core on the reel, so that it is substantially impossible to guide the standby reel on to the unwinding spindle, the function of which must therefore be performed by the swing arm spindle of the transfer device itself. As a result, the transfer arm is not freed until the reel runs out, thus complicating the design of the transfer device. Lastly, unless the standby reel is wound tightly, the turns in the strip may slip when accelerated up to the speed of the runout reel, thus resulting in "bags" forming in the strip and, particularly in the case of narrow reels, in oscillation of the reel in turn resulting in fallout and tearing of the strip, etc.